1. Field of the Invention
The present invention relates to a central lock for multi-point safety belts or safety harnesses. The central lock includes a housing with several insertion openings distributed over the circumference of the housing. Tongues connected to the belts can be inserted into the insertion openings. A holding plate for holding bolts interacting with the tongues is fixed in the housing. A rotatable release member mounted outside of the housing is provided for axially displacing a release plate against the force of a restoring spring. A mechanism is arranged between the release member and the release plate for transforming the rotary movement of the release member into an axial displacement of the release plate.
2. Description of the Related Art
Safety belts which include a lap belt and additional shoulder belts as well as crotch belts, also called four-point, five-point or six-point belts, are usually equipped with so-called central locks. Such central locks have on the circumference thereof slot-like insertion openings in which the belts can be anchored by means of tongues attached to the belts. By actuating opening mechanisms, all or a certain number of the belts are released in such a way that the user of the harness can remove the belts without further impairment. The opening mechanisms are actuated by means of wing-like release members which are mounted in the center of the central locks. The release members can be rotated in both directions for actuating the opening mechanisms. Therefore, they are also called rotary locks. The tongues are anchored in the central locks by means of cylindrical holding bolts which engage under the load of a spring in bores of the tongues. Another possibility of anchoring is provided by rocker-type latches which engage in corresponding recesses in the tongues. In order to release the tongues, the holding bolts or the latches must be displaced axially by a predetermined dimension. For this purpose, the rotary movements of the wing-like release members are transformed into axial movements.
In accordance with a known embodiment, the principle of the inclined plane is utilized for transforming the rotary movements into axial movements. For this purpose, a spring-loaded release plate is arranged in the central lock. A projection in the shape of a tubular piece is arranged in the center axis of the release plate. The projection has four inclined planes arranged uniformly distributed over the circumference. Always two oppositely located inclined planes extend in opposite directions. Each plane forms a quarter helix. The release member is provided with a center axle which extends through the tubular projection of the release plate and which has at its end slide members which accurately correspond to the inclined planes. When the release member is rotated, the rotary movement is transformed into an axial movement as a result of the fact that the sliding members slide on the inclined planes. This results in a positively guided axial movement of the release plate.
In accordance with another embodiment, the sliding members are formed by a pin which transversely extends through the center axle of the release member and which slides with its end portions on the inclined planes.
The axial movement produced in this manner raises the release plate, so that the holding bolts are moved out of their holding positions and release the tongues.
Because of practical considerations, it is desirable to keep the structural height of such central locks low. The structural height of such locks is additionally limited by certain regulations, for example, the safety standards of racing cars FIA 8854 (Federation Internationale du Sport Automobile). In accordance with this regulation, the maximum diameter of the central lock is 71 mm.
For the above reasons, the diameter of the tubular central axles must be kept small in order to be able to accommodate the entire opening and anchoring mechanism for the tongues while taking into consideration the required cross-sections depending on the breaking load. However, the smaller this diameter is selected, the steeper the incline of the inclined planes must be in order to achieve the necessary axial displacement.
The angle of actuation of the rotary locks is usually a maximum of 90.degree.. Some safety standards require additional free paths for the release member of at least 25.degree. before activation of the opening mechanisms occurs. This means that there remain a maximum of 65.degree. for the inclined planes for obtaining the desired axial displacements. While it can be simply assumed that, starting from a 45.degree. inclination of the sides of the inclined planes, the force required for opening is equal to the axial force, this does not take into consideration the friction losses between the sliding blocks or pins and the sides of the planes.
In the embodiment utilizing a pin and inclined planes, only a linear contact exists between the two structural components which leads to the problem that the frictional losses are significantly increased as soon as any sliding/lubricating agent has been used up, has become resin, has been washed out under unfavorable environmental influences or has been contaminated as a result of the influence of dust and, thus, acts more like a grinding agent. This means that after the lock has been in use for several years, wear may occur which impairs the operation of the lock. Damage to the sliding surfaces leads to increased corrosion and abrasion and the attendant increase of frictional forces. This increase causes a direct linear increase of the force required for opening.
The inclined planes of the known embodiments are inclined linearly, so that the opening forces are constant. However, the spring forces which close the opening mechanisms have at least a linearly increasing force characteristic, so that the required opening forces of the central locks increase continuously during opening as a result of the superposition of forces.
The safety standards to be applied when testing such central locks require, in order to prevent unintentional opening, a minimum opening force of a lock which has not been subjected to a load resulting from an accident. The maximum opening forces are limited in order to be able to open the central lock without problems after a load resulting from an accident. The required force limits are between .gtoreq.10N and .ltoreq.60N.